Field
The present invention relates to systems and methods for transferring micro devices. More particularly, embodiments of the present invention relate to systems and methods for rotationally aligning an array of micro devices relative to a substrate.
Background Information
The feasibility of commercializing miniaturized devices such as radio frequency (RF) microelectromechanical systems (MEMS) microswitches, light-emitting diode (LED) display systems, and MEMS or quartz-based oscillators is largely constrained by the difficulties and costs associated with manufacturing those devices. Miniaturized device manufacturing processes typically include processes in which miniaturized devices are transferred from one wafer to another. In one such implementation, a transfer wafer may pick up an array of miniaturized devices from a donor wafer and bond the miniaturized devices to a receiving wafer.
Miniaturized device transfer requires accurate and repeatable alignment in six spatial degrees of freedom between the transfer wafer and target wafer during the pick-up and bonding processes. Furthermore, alignment between the transfer wafer and the target wafer may be required after making contact between the target wafer and the transfer wafer. Methods and apparatuses for aligning two flat surfaces in a parallel orientation have been described, and may be applied to the problem of miniaturized device transfer. However, using some of the described methods, the wafers, or miniaturized devices on the wafers, may be smeared and damaged if alignment occurs after making contact between the wafers. This smearing may be caused by parasitic lateral motion, which is lateral motion of a point on an object accompanying rotation of the object about a center of rotation. That is, unless the point coincides with the center of rotation, the point will experience some lateral motion relative to the center rotation as it effectively pivots about the center of rotation. Some systems, such as hexapod robots, hybrid split-axis stages with tripod robot, and six-jointed serial arm robots, may use real-time motion control to provide rotational alignment about a point at the intersection of two planar surfaces, with negligible parasitic motion. However, such systems have some combination of limitations that may include slow response, inadequate stiffness, high cost, and excessive size and/or space requirements.